To prevent undesired traffic (and specifically, traffic loops) in MPLS networks comprising E-tree structures for serving specific traffic flows/services, a so-called “Split Horizon” (SH) rule has been formulated in the prior art.
An MPLS network may comprise one or more geographical, technological and/or administrative network domains.
An E-tree structure in a communication network section may be established on one or more network domains for a specific traffic service, the E-tree being characterized in that it comprises at least one root node (say, a central office of a bank), which may be connected to two or more leaf nodes (branches of the bank) directly or via other transit nodes in the network. If the bank central office has a protection server, the server may have another geographic location and will form a second root of the E-tree.
It can be mentioned that E-Tree is a standard name for point-to-multipoint (P2MP) traffic services.
The SH rule states that the root may be in bidirectional communication with any of the leaves in the E-tree structure, while leaves of the E-tree cannot be in communication with one another. Following these rules actually allows preventing main causes for traffic loops in any E-three structure.
In other words, for E-tree services, communication between leaves is not allowed, while communication between each of the roots and all leaves of the structure is required.
Prior art comprises various studies of the problem, and attempts to practically implement the SH rule to prevent traffic loops and communication between leaves in communication networks.
For example, the work of Simon Delord et al. “MEF E-tree service over MPLS. Needs, Myths and Challenges” from a site called http://www.ethernetacademy.net/ discusses the SH rule, saying that on E-tree each endpoint is designated as either a root or a leaf. Root can communicate with all other endpoints on the E-tree, however leaf can only communicate with roots but not leafs. However, the article does not comprise practical recommendations how to implement the rule in the network.
US2007177661A describes a method for detecting a network loop problem in a network, which includes: selecting a known static address of a selected device which should normally be detected at not more than one port of a downstream device; determining if the static address is detected in more than one port in a downstream device, wherein the current downstream device includes a first port which normally detects the known static address and a second port; if the static address is detected at the second port of the current downstream device, then determining the connection to the second port and if the connection to the second port is a leaf, then identifying the leaf as a misbehaving node, and if the connection to the second port is not a leaf, then evaluating a next downstream device.
Prior art also comprises a concept (previously presented by the Applicant) for marking different domains of a communication network with different categories/marks for preventing loops there-between. US2010080239A describes a technology for combating loops in multi-domain networks, by assigning to network domains categories, at least such as “high/trusted” and “low/less trusted”, and by making a decision about relearning Forwarding Information Base FIB of any edge node interconnecting different network domains, utilizing the assigned categories.
Those skilled in the art know that in complex communication networks which form a mesh and comprise a number of network domains, the task of preventing loops is quite complex and painstaking.
Modern MPLS networks, such as VPLS (virtual private LAN service) are mesh networks which usually support E-tree services. Any MPLS network, for example a Hierarchical VPLS network may comprise/serve multiple E-tree services which usually utilize/cover overlapping portions of the network.
To the best of the Applicant's knowledge, no simple, user-friendly, automatic measures have been proposed for E-tree services in VPLS and HVPLS networks by now, to facilitate prevention of traffic loops.